Bosch 500 series. I think all of the Bosch ovens come in 27" as well as 30". They also claim to have the largest interior of 27" ovens on the market, which is why I bought mine. Love it.

Miele has both their Chef and MasterChef ovens in 27".

Ajmadison lists 36 27" wall ovens. Here they are sorted by price low to high.

Here is a link that might be useful: Ajmadison oven list

I have the Bosch 500 series 27" wall oven and find it quite roomy inside. No regrets here.